Tillage that is deeper and more thorough is classified as primary, and tillage that is shallower and sometimes more selective of location is secondary. Primary tillage such as ploughing tends to produce a rough surface finish, whereas secondary tillage tends to produce a smoother surface finish, such as that required to make a good seedbed for many crops. Harrowing and rototilling often combine primary and secondary tillage into one operation.
Puddling is the tillage of rice paddies while flooded, an ancient practice that is used to prepare for rice cultivation. Historically, this has been accomplished by dragging a weighted harrow across a flooded paddy field behind a buffalo or ox, and is now accomplished using mechanized approaches, often using a walking tractor. Puddling reduces the percolation rates of water by churning the clay particles and making them close many of the soil pores.
